This proposal will examine the relationship between diabetes-mediated impairments in insulin receptor (IR) signal transduction mechanisms, including insulin-stimulated protein phosphorylation and glucose transporter (GLUT) trafficking, and the development of cognitive deficits in diabetic subjects. The hippocampus is an important integration center for learning and memory in the mammalian central nervous system (CMS) and is particularly sensitive and responsive to changes in insulin concentrations. Insulin administration improves cognitive performance in a variety of physiological and pathophysiological settings, including diabetes. Conversely, decreases in IR expression and/or signaling may contribute to the development of diabetic encephalopathy, including cognitive deficits observed in type 1 subjects. Unlike the peripheral IR system, little is known about the functional role of IRs in the CMS and how the activity of the neuronal IR system may be impaired in diabetes phenotypes. In view of the emerging relationship between insulin and cognition and the importance of the hippocampus in cognition, the aims of this proposal are: 1) to establish the functional relationships of components of the IR system in the rat hippocampus, including phosphatidylinositol 3-kinase (PI3-K), mitogen-activated protein kinase (MARK) signaling and the insulin-sensitive GLUTs; 2) to determine whether the neurological consequences of diabetes include impairments in IR expression and/or signaling; 3) to determine whether downregulation of IR expression in the rat hippocampus produces impairments in IR/PI3-K/MAPK signaling and GLUT trafficking, thereby providing a mechanistic basis for decreases in behavioral performance observed in experimental models of type 1 diabetes. Successful completion of these studies will: 1) determine the signal transduction mechanisms of the IR system in the brain; 2) provide insight into the mechanisms through which insulin enhances cognitive function in physiological settings; 3) provide a fundamental mechanistic bridge between impairments in IR expression and/or signaling and the morphological, electrophysiological and cognitive deficits associated with type 1 diabetes.